1. Field of the Invention
The present invention relates to an apparatus for fabricating a liquid crystal display device, and more particularly, to a mask holder for irradiating UV-rays.
2. Discussion of the Related Art
A thin flat panel display tends to have a thickness of no more than a few centimeters and is operated at a low voltage. Such displays consume less power and are portable. Among them, a liquid crystal display device has been the most widely used in various fields such as a notebook computer, a computer monitor, a gauge monitor for spacecrafts and airplanes, and the like.
Such a liquid crystal display device, as shown in FIG. 1, generally includes a lower substrate 1 having a plurality of thin film transistors (not shown) and pixel electrodes 3 formed thereon, an upper substrate 2 having a black matrix layer 4, a color filter layer 6, and a common electrode 8, and a liquid crystal layer 5 between the lower and upper substrates 1 and 2. Electric fields are generated between the pixel and common electrodes 3 and 8 so as to drive the liquid crystal layer 5. Light transmittance is controlled through the driven liquid crystal layer 5 in order to display images on the display screen.
Moreover, alignment layers (not shown) are formed on the front sides of the substrates 1 and 2 for an initial alignment of the liquid crystals 5.
A sealant 10 is formed between the lower and upper substrates 1 and 2 so as to prevent liquid crystals from leaking out of the substrates and to bond the substrates to each other.
The sealant 10 is coated on the lower or upper substrate 1 or 2, and is then hardened after attaching the lower and upper substrates 1 and 2 to each other. Types of such sealants include a thermo-hardening sealant and a UV-hardening sealant, which are hardened by heat and UV-rays, respectively.
Meanwhile, the type of sealant may be selected from one of the thermo-hardening sealant and the UV-hardening sealant depending on the method of fabricating a liquid crystal display device.
In a vacuum injection method for injecting liquid crystals in the attached substrates using a capillary phenomenon and a pressure difference, the sealant is hardened before the liquid crystals are injected after attaching the lower and upper substrates to each other. There is no chance of contaminating the liquid crystals even if the sealant leaks out. Hence, the vacuum injection method mainly uses the thermo-hardening sealant.
In the liquid crystal dropping method, the attaching process of two substrates is carried out after dispensing the liquid crystals on one of the substrates 1 and 2. The sealant is hardened after forming the liquid crystal layer. Hence, when the thermo-hardening sealant is used, the sealant flows out during a heating process, thereby contaminating the liquid crystals. Therefore, the UV hardening sealant is mainly used for an LCD formed by the liquid crystal dropping method.
FIG. 2 is a perspective view illustrating a UV emitting device for hardening a UV-hardening sealant in a liquid crystal display device using the liquid crystal dropping method of the related art.
Referring to FIG. 2, a UV emitting device of the related art includes a substrate stage 20 and a UV source unit 30 having a UV lamp 32 placed over the substrate stage 20.
A hardening process of a sealant using such a UV emitting device of the related art is carried out in a manner that UV-rays are irradiated by the UV source unit 30 to attached substrates 1 and 2 loaded on the substrate stage 20 of the UV emitting device. In this case, a UV-hardening sealant 10 is formed inside the attached substrates 1 and 2.
In the UV emitting device of the related art, the UV-rays from the UV source unit 30 are irradiated to the entire surface of the substrate stage 20 on which the attached substrates are loaded. Thus, the UV-rays are irradiated onto the entire exposed surface of the attached substrates.
However, once the UV-rays are irradiated to the entire surface of the attached substrates, characteristics of devices on the substrate, such as thin film transistors and the like, are degraded. Moreover, a pre-tilt angle of the alignment layer for an initial alignment of the liquid crystals is changed.